Enzymes for the MCAT: Everything You Need to Know - Shemmassian Academic Consulting (2023)

(Note: this guide is part of ourBiochemistry MCAThe would be.)

Part 1: Introduction to enzymes

Part 2: General characterization of enzymes

a) catalytic activity

b) Enzyme-substrate binding

c) Types of enzymes

d) Cofactors, coenzymes from vitamins

e) Catalytic amino acids

Part 3: Enzyme kinetics and inhibition

a) Michaelis-Menten e Lineweaver-Burk

b) competitive inhibition

c) Non-competitive braking

d) Mixed and non-competitive braking

Part 4: Enzyme Activity Regulation

a) Local environmental conditions

b) Covalent modification

c) Allosteric regulation

d) Zimogenia

e) Cooperation

f) Feedback adjustment

Part 5: High Performance Conditions

Part 6: Practical passage of enzymes

Unit 7: Practical questions and answers about enzymes

Part 1: Introduction to enzymes

Enzymes are one of the mostheavily testedscience topics on the MCAT and are an important part of our daily lives. Every cell in our body performs many of its functions with the help of enzymes, and the misregulation of these enzymes is responsible for a wide range of human diseases, such as cancer and hypertension.

Many students struggle with enzymes on the MCAT, often missing valuable points on questions that test topics ranging from enzyme inhibition to feedback regulation. In this guide, we'll give you what you need to know - no more, no less - to test enzymes for MCAT. All terms in bold throughout the guide will be defined in Part 5 of the guide, butwe encourage you to create your own definitions and examples as you browse this resource to make them as meaningful as possible.Ty!

In addition to knowing the content, you also need to know how to do it. review various graphs, equations, and enzyme-related terms presented by the MCAT. At the end of this guide is an excerpt on MCAT-style enzyme exercises and self-contained questions that will test your knowledge and show you how the AAMC likes to ask questions.

Let's start!

Part 2: General characterization of enzymes

a) catalytic activity

Enzymes are biological catalysts, acatalystis defined as a substance that accelerates the rate of a chemical reaction without being consumed. For example, suppose you need to get from point A to point B and the two points are 10 miles apart. You could walk, which will probably take some time. Or you can go by car and get there much faster. In this case, the car acts as our catalyst. Attention, the distance does not change, buthow fast will you get thereit's faster.

Just as a car speeds up our transportation, an enzyme is used to speed up the rate of a biochemical reaction. As a result, the enzyme is classified asbiological catalyst, which has the following properties (let's dive deeper into each of them):

• Reduces the activation energy of the reaction

• Affects reaction kinetics but not thermodynamics (∆G) or equilibrium constant

• regenerates

Let's look at activation energy first. Which of the following activities requires more energy: walking or driving 10 miles? If you said walking, you're right. (In a car, just step on the accelerator!) The enzyme – in our example, the car – reduces the amountinput energynecessary for a chemical reaction to take place. By decreasing the input power, oractivation energyreaction, the reaction can occur much more quickly. This brings us to reaction kinetics.

The enzyme affectskineticsreaction by increasing the reaction rate. make a notereaction speedis the rate at which reactants are consumed or the rate at which products are formed. It is important to note that enzymes DO NOT affect the thermodynamics (∆G) or the equilibrium constant of the reaction.

Let's look at another example to illustrate this point. We have a machine that turns red balls into red cubes. Normally, if you give the machine 10 red balls, it will produce 5 red cubes in 1 hour. Now let's assume the machine is driven by a catalyst - if you give the machine 10 red balls, it will produce 5 red cubes in 1 minute.

This affects the kinetics of the machine, as it can now run faster, but the thermodynamics and equilibrium constant remain the same. In each case, 10 red balls make 5 red cubes, no matter how fast the machine can do it.

Below, we illustrate these effects in a commonly drawn reaction diagram:

Finally, there are enzymesregeneratedduring their catalytic cycles. This is very important because regeneration reduces the amount of protein the cell needs to produce to carry out biochemical reactions. For example, cells useVeryATP, and most of that ATP is produced by ATP synthase, an enzyme. (In summary, enzymes usually end in-ase!) If each ATP synthase could synthesize just one ATP molecule, the cell would be overrun with ATP synthase enzymes. The ability of each ATP synthase – and other enzymes – to reset itself after each cycleabsolutely essentialfor our survival.

In the figure below, we show how regeneration would have a huge impact on the number of ATP synthases needed by the cell if the cell could not regenerate during many catalytic cycles.

b) Enzyme-substrate binding

We've already talked about the general properties of enzymes, and now let's delve into more essential details. We often talk about chemical reactions by writing reaction diagrams like A → B → C. For enzymes, we can draw a reaction diagram to help us better understand what exactly is going on, and it goes something like this:

E + S → ES → E + P

E = enzyme

S = substrate

P = product

We'll come back to the general reaction scheme when we look at enzyme inhibition in the next section, but let's focus on the ES, or enzyme-substrate complex.

There are two models to describe the enzyme-substrate complex: 1)model with keyholeeu 2)induced fit model. The lock and key model describes the substrate as the "key" and the enzyme as the "lock". Without changing any conformation, the key must fit perfectly in the lock so that the two can fit together.

The induced fit model (which is generally the most accepted model) states that the conformations of enzymes and substrates need not be as rigid as the lock and key model suggests. Instead, after the substrate binds to the enzyme, the two will undergo slight conformational changes to improve their binding to each other.

c) Types of enzymes

There are six well-known types of enzymes that the MCAT wants to know about: